As optical disc media (information recording media), a compact disc (registered trademark; hereinafter referred to as a CD) and a digital versatile disk (hereinafter referred to as a DVD) have been frequently employed. In recent years, not only a read-only optical disc, but also a writable DVD-Random Access Memory (hereinafter referred to as a DVD-RAM), a write-once DVD-Recordable (hereinafter referred to as a DVD-R), and a DVD-Rewritable (hereinafter referred to as a DVD-RW) have attracted attention.
The DVD-RAM disk is characterized by that it is able to perform recording and playback by random access, and therefore, it is suitable as a DVD recorder and an information storage medium. Further, during recording and playback in/from the DVD-RAM disk, the cycle of a reading clock during playback and the cycle of a writing clock during recording are controlled with reference to wobbles that are carved at regular intervals along recording tracks on the DVD-RAM disk as shown in FIG. 23(a), and a laser power for recording is controlled to a power suitable for recording of normal data on the basis of wobble amplitude information that is the amplitude value of a wobble signal component, in order to ensure the quality of recorded data even when flaws or stains are present on the recording surface. As a typical application of this technique, there is ROPC (Running Optimum Power Control) that is used when recording data on a recordable optical disc such as a CD-R (Compact Disc-Recordable). The principle and means thereof are specifically described in “CD-WO System Description Ver.2.0. Further, address information (Complementary Allocated Pit Addressing: hereinafter referred to as CAPA) of an embossed area has previously been recorded on the DVD-RAM disc as shown in FIG. 23(a), and the address information detection capability is one of factors that determine the random-access performance and the recording/playback performance.
Hereinafter, a description will be given of a wobble amplitude information detection method, a recording laser power appropriate control method, and an address information detection method of the conventional DVD-RAM disk recording/playback apparatus.
FIG. 24 is a block diagram illustrating the conventional DVD-RAM disk recording/playback apparatus.
With reference to FIG. 24, optical pickup 3 performs recording and playback of digital data into/from an optical disc medium which is a means for holding the digital data. The optical pickup 3 comprises a laser generation circuit 4 comprising a semiconductor laser; a four-split photodetector 5 for generating a tracking error signal, which receives a light beam outputted from the laser generation circuit 4 and reflected at an optical disc medium 1, and converts the power of the optical beam into an electric signal; and a two-split photodetector 6 for generating a focus error signal. Further, the optical pickup 3 is mounted on a transfer stage (movable stage) which is movable in the direction of the radius of the optical disc medium 1, and performs a focus servo for focusing the light beam outputted from the laser generation circuit 4 onto the tracks formed on the optical disc medium 1 through an objective lens as shown in FIG. 2, and a tracking servo for controlling the light beam to scan the tracks, according to a control command which is supplied from an optical disc controller 16 through an optical pickup driving circuit 18. In addition, the optical pickup 3 performs an operation for seeking a target address by moving the transfer stage in the direction of the radius of the optical disc medium.
The optical disc medium 1 has plural tracks extending along the circumference thereof. As shown in FIG. 3(a), each track is divided into sectors as units of data recording, and each sector has, at its beginning, an address area (CAPA area) in which an address for identifying the sector is recorded. Further, each sector has a data area in which playback data are stored, which data area follows the CAPA area. Immediately after the CAPA area, i.e., between the CAPA area and the data area, there is provided a gap area in which no data to be played exist and no data to be played are stored. The optical disc medium 1 is rotated at a predetermined rotation speed by an optical recording medium rotation control circuit 2, and data are recorded thereon according to the power of the light beam outputted from the laser generation circuit 4.
I/V converters 7 to 10 are current-to-voltage converters for converting the detected currents outputted from the four-split photodetectors 5a to 5d into voltages. An adder 11 adds the output voltage from the I/V converter 7 and the output voltage from the I/V converter 10 to add the components outputted from the areas 5a and 5d of the four-split photodetector 5, which are parallel to the track direction. An adder 12 adds the output voltage from the I/V converter 8 and the output voltage from the I/V converter 9 to add the components outputted from the areas 5b and 5c of the four-split photodetector 5, which are parallel to the track direction. The output signal from the adder 11 and the output signal from the adder 12 are input to a light difference signal detection circuit 13. The light difference signal generation circuit 13 adjusts the amplitude balances of the output signals from the adders 11 and 12, respectively, and subtracts the output of the adder 12 from the output of adder 11 to generate a push-pull signal (light difference signal) 14. The push-pull signal 14 is input to a wobble amplitude detection circuit 158. On the other hand, since the push-pull signal 14 includes a high frequency component, only a low frequency component of the push-pull signal 14 is detected by a low-pass filter (hereinafter referred to as LPF) 15 so as to treat the signal in a servo band, and the filtered signal is input to an optical disc controller 16 as a tracking error signal 17.
I/V converters 116 and 117 are current-to-voltage converters for converting the detected currents outputted from the two-split photodetectors 6a and 6b into voltages. A playback signal detection circuit 118 adds the output voltages from the I/V converters 7 to 10 which are the full output component from the four-split photodetector 5 and the output voltages from the I/V converters 116 and 117 which are the output component from the two-split photodetector 6, thereby generating a playback RF signal 119. The playback RF signal 119 is input to a signal processing circuit 159. The signal processing circuit 159 removes a high frequency noise component from the playback RF signal 119 by an equalizer and boosts a high frequency area of the RF component to improve the jitter of the playback RF signal, and performs slicing by a symbolic center level of the recorded digital data while controlling a playback clock synchronized with the clock component existing in the signal using a PLL (Phase Locked Loop) circuit, thereby demodulating a binarized signal 160.
A wobble amplitude detection circuit 158 detects a frequency component in which the tracks on the optical disc medium 1 wobble at a predetermined frequency, from the inputted push-pull signal 14, and detects an envelope with an analog signal processing circuit to output it as a wobble amplitude signal to a low-speed analog-to-digital converter 161. The low-speed analog-to-digital converter 161 converts the signal supplied from the wobble amplitude detection circuit 158 into a digital signal, and outputs the digital signal to a reflected light control circuit 162.
The reflected light control circuit 162 obtains a laser power suited to recording on the basis of variations in the inputted wobble amplitude signal, and controls the power of the laser outputted from the laser generation circuit 4 to the power suited to recording via a driving circuit 163. The driving circuit 163 receives a fundamental recording pulse 114 for recording target digital data, which is outputted from the optical disc controller 16, and generates a recording laser power control signal 115 as shown in FIG. 3(d) according to a command outputted from the reflected light control circuit 162. The laser power of the laser generation circuit 4 changes according to the recording laser power control signal 115.
The optical disc controller 16 performs generation of various control signals required for the optical disc recording/playback apparatus such as a focus servo for focusing the light spot of the laser beam outputted from the laser generation circuit 4 through the optical pickup drive circuit 18, a tracking servo for performing position control so that the light spot scans the tracks, seek operation for random access, and rotation control for the optical disc medium 1 using the optical recording medium rotation control circuit 2, as well as processings such as encoding and decoding of the recorded digital data, on the basis of the tracking error signal 17, the binarized signal 160 demodulated from the playback RF (Radio Frequency) signal 119 (described later), the address polarity information 60 extracted from the CAPA area, and the address position information 61. The optical disc controller 16 mentioned above is an optical disc controller disclosed in International Application No. WO01/08143 (Patent Document 1), and it includes a servo microcomputer, a control microcomputer, a recording information generation circuit, a recording waveform generation circuit and the like (refer to description corresponding to FIG. 2 disclosed in Patent Document 1).
Hereinafter, with reference to FIGS. 3(a)-3(d), a description will be given of an operation for controlling the recording laser power to an optimum value, when defects due to flaws and stains exist on the recording surface of the optical disc medium 1.
As shown in the figure, the light spot moves along the track. In FIG. 3(a), an elliptical shaded area is a defect area due to flaws or stains. FIG. 3(b) shows a recording gate signal 19 in which “H” indicates the recording state while “L” indicates the playback state. In the playback state where the recording gate signal 19 is “L”, the power of the laser outputted from the laser generation circuit 4 is changed to a power suited to playback. FIG. 3(c) is a timing chart illustrating change in the wobble amplitude signal, i.e., change in the power of the reflected light from the optical disc medium 1, which change occurs when the light spot obtained by focusing the light beam on the track scans the track shown in FIG. 3(a). If the defect exists in the data area, the power of the reflected light, is lowered from level Pr0 to level Pr1 when the light spot passes over the defect. FIG. 3(d) is a timing chart schematically showing the level change in the emission power of the laser, i.e., the laser power, which is controlled by the above-mentioned laser power control method. The dotted lines in the vertical direction shown in FIG. 3 show the temporal relationships among the position of the light spot, the timing chart of the power of the reflected light shown in FIG. 3(c), and the timing chart of the laser power shown in FIG. 3(d), when the light spot is positioned in the respective areas shown in FIG. 3(a).
With reference to FIG. 3(d), in period T1 during which the light spot passes the gap area, the laser generation circuit 4 performs test emission for low-speed power switching. During this test emission, in the example shown in FIG. 3(d), two values of powers, power Pkt and power Pbt, are emitted, thereby performing fundamental optimum control for the laser power when performing recording that depends on temperature change or the like (refer to the description corresponding to FIG. 1 of Patent Document 1).
When the period T1 where the test emission is carried out is ended, the light spot enters the data area T2. In this period, as shown in FIG. 3(d), light emission is carried out such that high-speed switching is carried out among three values of powers (Pk, Pb1, Pb2) for performing accurate recording. These three values of powers are obtained by an emission light control circuit which is not shown in FIG. 24 (refer to the description corresponding to FIG. 1 of Patent Document 1).
When the light spot is passing over the defect, the power of the optical output or the laser is partially scattered or absorbed by this defect, whereby the power deviates from the optimum power for recording digital data on the optical disc medium 1. As a result, the power level of the reflected light from the optical disc medium 1 is lowered from the power Pr0 in the case where no defect exists, to the power Pr1. In response to this reduction, the loss in the level of the power of the reflected light due to the defect is detected from the wobble amplitude signal in period T3 during which the light spot crosses the detect, and the laser power is controlled to compensate this loss.
Using the circuits mentioned above and the operations thereof, it is possible to control the laser power to an appropriate value so as to improve the recording quality of the digital data against change in the envelopment such as temperature, and partial change due to flaws and stains.
Next, a description is given of an operation of detecting address information in the DVD-RAM disk.
In order to detect address information in the DVD-RAM disk, it is necessary to input the push-pull signal 14 into an address information detection circuit 59 for detecting such as address polarity information 60 and address position information 61. The address information detection circuit 59 detects the position of the front-side CAPA (front CAPA) as address polarity information 60 on the basis of the push-pull signal 14 shown in FIG. 23(b) and the threshold level shown by the upper dotted line in FIG. 23(b), and detects the position of the rear-side CAPA (rear CAPA) as address polarity information 75 on the basis of the push-pull signal 14 shown in FIG. 23(b) and the threshold level shown by the lower dotted line in FIG. 23(b). Further, the address information detection circuit 59 adds (OR operation) the address polarity information 60 and the address polarity information 75 to generate address position information 61. As for the specific construction of the address information detection circuit 59, refer to the description relating to FIGS. 3 and 4 of Japanese Published Patent Application No. 2001-243714 (Patent Document. 2).
In the above-described conventional construction, however, when extracting the wobble amplitude information and the address information, the multipliers of the filters and the signal processing circuits included in the respective detection circuits must be varied for every recording/playback speed. Especially when digital data are recorded at high speed, the detection sensitivity of the wobble amplitude information is lowered by degradation of the detection accuracy due to variations depending on the temperature and the constituents and by burden of the processing of the digital signal processing circuit that operates with reference to a fixed clock, whereby appropriateness of laser power control during recording is undesirably disordered.
Further, a difference in frequencies between the wobble amplitude information as a low frequency component and the address information as a high frequency component is large. Therefore, in order to realize a recording speed range from a low speed to a high speed in the same circuit, the circuit control is complicated and, simultaneously, the circuit scale and the power consumption are increased in accordance with the recording speed.